One of the major problems in hypodermic syringe construction is the needle hub which forms a connecting unit between a hypodermic syringe barrel and a puncturing cannula. Numerous types of hub designs have been proposed to provide reliable and very firm connection between the cannula and the needle hub. The hub must also provide a very reliable seal with the syringe barrel's tapered adapter. Different materials have been used in the past for needle hubs. Polypropylene has been used for hubs, but has very little adherence to epoxies or other adhesives used to join the hub and cannula. Because of this shortcoming of polypropylene, various attempts have been made to mechanically anchor the epoxy to the hub. Epoxy will bond readily to the metal cannula, but not to the polypropylene hub. Difficult to mold undercut pockets have been proposed in U.S. Pat. No. 3,179,107, as well as expensive separate holding sleeves as in U.S. Pat. No. 3,472,227. Various other types of crimped anchoring structure such as in U.S. Pat. No. Re. 28,713 and 2,844,149 have been proposed for securing a metal cannula to a thermoplasitc needle hub.
Nylon has also been used in hubs because it has very good adherent properties to epoxy. No expensive undercut structure was required in the nylon hub. However, nylon tends to readily absorb moisture when subjected to elevated temperatures or humid environments and such absorbed moisture tends to slightly alter the hub's dimensional configuration, sometimes causing the hub to become loosened on the tapered adapter of the syringe barrel during long storage periods.